1. Field of the Invention
The invention generally relates to systems and methods of detecting cancer and, more specifically to an near infrared photonic prostatoscopy analyzer.
2. Description of Prior Art
The common screening tests for prostate cancer diagnosis are digital rectal examination (DRE), prostate specific antigen (PSA) blood test, and the transrectal ultrasound (TRUS) imaging. A value of PSA over 4.0 ng/ml is the commonly used threshold for further diagnostic evaluation. Although PSA test appears to have acceptable sensitivity for late stage cancer and disease with histopathologic features associated with tumor progression of a large volume, poorly differentiated cells and extracapsular penetration, its accuracy is limited as low as 28%-35%. During the DRE, a doctor inserts a lubricated gloved finger into the patient's rectum to feel for the enlargements and hard areas of prostate that might indicate prostate cancer. DRE has a reported sensitivity of 18%-22%. TRUS is no longer considered as a first-line screening test for prostate cancer because of its poor spatial resolution and contrast, but it does play a role in mapping the locations of the biopsy sampling. The confirmation of prostate cancer finally needs a needle biopsy of the prostate. In the biopsy, a number (12-18) of cores of prostate tissue are randomly taken from whole region of the prostate using a thin needle with the help of TRUS to map the locations of the sampling.
The early detection and treatment of prostate cancers can significantly reduce mortality. Conventional oncology imaging methods for prostate cancer diagnosis still depend on bulk physical properties of cancer tissue and are not effective for early-stage primary tumors. Since PSA and DRE have limited accuracy, TRUS has poor contrast between normal and abnormal tissue regions, and needle biopsy is invasive and may cause damage to the prostate, it is highly desirable to develop a better method which is accurate, of higher spatial resolution, and non-or-less invasive for prostate cancer screening.
Optical imaging technique using near infrared (NIR) light from 650 nm to 2,400 nm in the four tissue optical windows (Window #I, 650 nm-950 nm; Window #II, 1,100 nm-1,350 nm; Window #III, 1,600 nm-1,870 nm; and Window #IV, 2,100 nm-2,300 nm) as shown in FIG. 4 provides an attractive noninvasive approach for screening human diseases [1]. These four “tissue optical windows” in the NIR range, which correspond to lower absorption of major tissue chromophores such as water, oxygenated and deoxygenated hemoglobin, allow light to penetrate deeply into the tissue up to several centimeters. As indicated in FIG. 4, the tissue scattering is much less in windows #II-#IV reducing image blurring. The other main advantages of the NIR optical approaches are its low-cost, the ability to monitor multiple independent optical reporters simultaneously in vivo using light with different wavelengths, the absence of radioactive intermediates, and the relative simplicity of the imaging hardware as compared with. Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) equipment. These advantages make optical imaging unmatched by any other in vivo imaging techniques. The major disadvantage of the optical imaging approaches is that high scattering of biological tissue causes most photons to diffuse. A very small percentage of ballistic and snake photons makes direct imaging practically only in surface layers of tissue. Scientists have to use the four NIR tissue windows for deep imaging and reducing the image blurring, and explore optical tomography methods and/or inverse image reconstruction approaches to obtain 3D images of target organs and locate the three dimension (3D) positions of the abnormal tissue and recover the 3D spatial distribution information of optical parameters of the whole tissue. When light transports in a highly scattering medium such as tissue, the blurred transmission or backscattered images are rendered to us. The behavior of diffusion essentially depends on optical properties of the tissue medium such as scattering coefficient (μs), anisotropy factor (g) and absorption coefficient (μa). Since the transmittance and backscattered images are acquired from those photons surviving passage from the tissue, which may contain clues about their voyage and the optical coefficients of the tissue, the measured light intensity distribution on the boundary of the turbid medium can be used to generate a map of the μs and μa of the whole tissue medium using an inversion algorithm.
To reduce image blurring and improve image quality, the four NIR tissue windows from 650 nm to 2,400 nm can be used. The CCD/CMOS cameras used to detect light in these four NIR windows can be Si-based (response for the spectral range of 400 nm-1,000 nm), InGaAs-based (1,000 nm-1,800 nm) and InSb-based (1,000 nm-5,000 nm) cameras. The tissue scattering is less for the longer NIR wavelengths as the scattering cross section (σs) is proportional to 1/λn, where n>1 for λ>400 nm. FIG. 4(a) shows the spectra of the total attenuation coefficient (μt) from the normal prostate tissue using the #I, #II, #III and #IV NIR windows, and FIG. 4(b) shows the spectra of the total attenuation length (lt) in μm from normal and cancerous prostate tissues using the #I, #II, #III, and #IV NIR tissue optical windows, where lt is inversely proportional to μt.
The important absorption biochemical components (chromophores) in tissue that can be detected in the absorption measurements are water (H2O), oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb). Since cancerous and normal prostate tissues have different water contents due to the development of cancer, the change of absorption and relative contents of H2O can be used as a potential fingerprint of native biomarkers to distinguish cancerous and normal prostate tissues [1]. Other critical native biomarkers are HbO2 and Hb, and changes of their relative contents are also sensitive to the cancer evolution. As a tumor grows, it rapidly outgrows its blood supply, leaving portions of the tumor with regions where the oxygen concentration is significantly lower than in healthy tissue regions. The change of the relative contents of HbO2 and Hb is usually measured using an oxygen saturation factor, which is defined as SO2═CHbO2/(CHbO2+CHb), where the CHbO2 and CHb are molar concentrations of HbO2 and Hb in tissue, respectively. The lower value of SO2 in a tissue area may indicate the existence of tumor in the area. Tumor hypoxia is the situation where tumor cells have been deprived of oxygen, and may be used to help diagnosis of tumors/cancers. As a result, change of water contents and values of SO2 (hypoxia) in prostate tissue areas obtained from the absorption and/or imaging measurements can be used as potential fingerprints of native biomarkers to evaluate existence and obtain 3D location of cancer areas.
To obtain a 3D image and locate the 3D position of cancerous prostate tissue embedded in normal prostate tissue, a portable rectal NIR scanning polarization imaging unit with an optical fiber-based rectal probe was developed and tested using NIR light ranged from 650 nm to 2400 nm. This transrectal scanning polarization imaging system was used to obtain 3D images and locate the 3D positions of abnormal prostate tissue hidden in normal prostate tissue based on differences of optical parameters between cancerous and normal prostate tissues. The scanning polarization imaging system can be used to acquire a set of 2D images by sequentially scanning a polarized illuminating light beam at different areas of a prostate gland through rectum, and obtain the distribution of light intensity backscattered from the prostate using a CCD/CMOS camera. An Independent Component Analysis (ICA)-based inverse image reconstruction algorithm was improved specifically for the application of backscattering configuration and used to obtain 3D images and locate the 3D positions of foreign inhomogeneities from the recorded array of the 2D images. Therefore, NIRPPA may introduce a new criteria/indicator for prostate cancer screening in addition to the conventional examinations to enhance the accuracy of prostate cancer detection.